An active power distribution network impedance inverse-time protection method and system

Abstract

The application discloses an active power distribution network impedance inverse time-lag protection method and system, which comprises the following steps: collecting voltage and current of each switch along the line in real time, calculating fault component impedance as a starting criterion; each switch determines the setting impedance in a unified manner in advance, and the setting impedance is the line impedance of the longest continuous three sections downstream from the self-protection installation multiplied by a reliable coefficient; after the fault is started, full-amount voltage and current phasor are extracted to calculate full-amount measurement impedance; the action time is determined according to the full-amount measurement impedance and the setting impedance according to the impedance inverse time-lag equation of the upper arch characteristic; when the measurement impedance exceeds the setting impedance, the protection is not locked, and the same equation is used to calculate the extended action time; each switch is independently timed, and the switch closest to the fault point has the shortest action time and trips first. The fault component is started, the full-amount measurement impedance is used as the distance criterion, the whole line is uniformly set, no communication is needed to form the time difference, the protection is fast in action, simple in setting and has no protection dead zone, and is suitable for the power distribution network containing high penetration rate distributed power sources.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection technology, and particularly relates to an active distribution network impedance inverse time protection method and system. Background Technology

[0002] The large-scale integration of distributed power sources such as distributed photovoltaics and small hydropower into the 10kV distribution network has transformed the traditional single-source radial distribution network into a multi-source active distribution network. When a short-circuit fault occurs in the system, distributed power sources provide short-circuit current to the fault point, changing the amplitude, direction, and distribution characteristics of the short-circuit current in the distribution network. This poses a serious challenge to traditional protection schemes based on a single-source radial structure design.

[0003] Currently, three-stage current protection (instantaneous overcurrent protection, time-limited overcurrent protection, and definite-time overcurrent protection) is widely used in 10kV distribution network feeders. This scheme, which uses current amplitude as the criterion, has the following problems: First, the amplification and diversion effect of distributed generation on fault current causes the fault current at each protection installation point to vary significantly with the connection location, capacity, and operating mode of the distributed generation, resulting in expansion and contraction of the protection range. This leads to insufficient sensitivity for remote faults and the possibility of cascading faults for near-end faults, making it difficult to balance various operating modes in the setting values. Second, the three-stage current protection relies on a fixed time difference of 0.3s to 0.5s to achieve coordination between upper and lower levels, resulting in long operating times. Furthermore, the coordination of these time differences is difficult to set in multi-segment, multi-branch active distribution networks. Third, inverter-type distributed generation is constrained by the current-limiting strategy of power electronic devices, and the short-circuit current is typically only 1.2 to 1.5 times its rated current. This further weakens the feeder fault current, severely reducing the sensitivity of protection based on current amplitude as the criterion, and even causing it to fail to operate.

[0004] Line longitudinal differential protection uses the sum of current phasors on both sides as the criterion, exhibiting absolute selectivity. However, it requires current transformers to be installed at both ends of the protected line and a dedicated communication channel to be laid, with strict synchronization of sampling at both ends. 10kV distribution networks have numerous feeder sections, T-connections, and complex line corridors. Upgrading to differential protection would require configuring communication and synchronization equipment for each section and branch, resulting in extremely high investment and maintenance costs, making large-scale application in distribution networks difficult. Furthermore, communication-based distributed protection and longitudinal comparative protection also rely on channel reliability; protection performance significantly degrades when the channel is abnormal.

[0005] Directional overcurrent protection uses directional elements to determine the direction of the fault to adapt to dual-end power supply. However, the weak feedback characteristic of inverter-type distributed power sources makes the fault current on the downstream side too small, and the sensitivity of the directional elements is insufficient. Moreover, when multiple distributed power sources are connected at multiple points, the direction of the fault current is complex, and the direction determination is prone to failure.

[0006] The fault component method decomposes the electrical quantities after a fault into a superposition of the normal state components before the fault and the fault-added components. By extracting the fault-added components, the influence of load current and steady-state output of distributed generation during normal operation is eliminated. The fault component impedance is defined as the ratio of the fault component voltage to the fault component current. Theoretically, the fault component network is a passive network where all power sources except the virtual power source at the fault point are short-circuited. However, in-depth analysis reveals that in the fault component network, both the system power source and the distributed generation are equivalent to their internal impedance. When a distributed generation is connected to the line between the fault point and the protection installation point, its internal impedance is connected in parallel to the connection point in the fault component network, changing the equivalent impedance from the protection installation point to the fault point. The distribution ratio of the fault component current in each parallel branch depends on the impedance ratio of each branch and varies with the protection installation location, making the relationship between fault component impedance and distance no longer a simple linear or monotonic relationship. Therefore, fault component impedance cannot be directly used as a reliable distance criterion for inverse-time protection in active distribution networks.

[0007] In summary, existing protection technologies have drawbacks such as difficulty in setting, insufficient sensitivity, long operating time, reliance on communication channels, and high construction and promotion costs under active distribution network conditions. There is an urgent need for a new feeder protection method that does not rely on communication, is simple to set, operates quickly, and can adapt to distributed power source access. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention proposes an active distribution network impedance inverse-time protection method and system. This method uses the fault component impedance as the fault initiation criterion and the total measured impedance at the time of the fault as the distance criterion. It employs an impedance inverse-time action equation with an upward-arching characteristic, and uses unified setting parameters for all switches along the entire line. This allows for the natural formation of time differences on feeders with multiple segments and distributed power sources without the need for communication channels, enabling rapid and selective isolation of fault sections.

[0009] In a first aspect, the present invention provides an active distribution network impedance inverse-time protection method, comprising: The protection devices of each switch along the line collect the voltage and current at the installation point in real time, calculate the fault component impedance, and determine that a fault has occurred and activate the protection when the fault component impedance meets the activation conditions. The fault component impedance is only used for activation and fault detection and is not used as the distance criterion for inverse time operation. The protection devices of each switch have their setting impedance determined in advance in a uniform manner. The setting impedance is set by multiplying the line impedance of the longest continuous three sections downstream from the protection installation point by a reliability factor, so that all switches on the entire line use the same value of the setting impedance. After the fault is initiated, the full voltage phasor and full current phasor at the time of the fault are extracted, and the full measurement impedance is calculated. The full measurement impedance is used as the distance criterion for inverse time action. Based on the full-scale measured impedance and the set impedance, the action time is determined using the inverse time equation of the upper arch characteristic impedance, wherein the inverse time equation of the upper arch characteristic impedance is a power function relationship between the action time and the full-scale measured impedance; When the full measurement impedance exceeds the set impedance, the protection does not lock out, and the extension action time is calculated using the inverse time equation of the upper arch characteristic impedance. The extension action time does not exceed the preset endpoint action time limit. The protection devices of each switch are timed independently according to the aforementioned action time. The total measured impedance of the switch closest to the fault point is the minimum value among all starting switches. The action time corresponding to the minimum value is the shortest action time among all starting switches. The switch corresponding to the shortest action time is the first to reach the action time and perform tripping.

[0010] Secondly, the present invention provides an active power distribution network impedance inverse-time protection system, comprising: The judgment module is configured to collect the voltage and current at the installation point of each switch along the line in real time, calculate the fault component impedance, and determine that a fault has occurred and start the protection when the fault component impedance meets the start-up conditions. The fault component impedance is only used for start-up and fault detection and is not used as the distance criterion for inverse time operation. The setting module is configured to pre-determine the setting impedance of the protection device of each switch in a uniform manner. The setting impedance is set by multiplying the line impedance of the longest continuous three sections downstream from the protection installation point by a reliability coefficient, so that all switches on the entire line adopt the same value of the setting impedance. The extraction module is configured to extract the full voltage phasor and full current phasor at the time of the fault after the fault is started, and calculate the full measurement impedance. The full measurement impedance is used as the distance criterion for inverse time action. The determination module is configured to determine the action time based on the full-scale measured impedance and the set impedance using the inverse time equation of the upper arch characteristic impedance, wherein the inverse time equation of the upper arch characteristic impedance is a power function relationship between the action time and the full-scale measured impedance; The calculation module is configured such that when the full measurement impedance exceeds the set impedance, the protection does not lock out, and the extension action time is calculated using the inverse time equation of the upper arch characteristic impedance, wherein the extension action time does not exceed the preset endpoint action time limit. The action module is configured such that the protection devices of each switch are timed independently according to the action time. The total measured impedance of the switch closest to the fault point is the minimum value among all starting switches. The action time corresponding to the minimum value is the shortest action time among all starting switches. The switch corresponding to the shortest action time is the first to reach the action time and perform tripping.

[0011] Thirdly, an electronic device is provided, comprising: at least one processor, and a memory communicatively connected to the at least one processor, wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the steps of the active power distribution network impedance inverse time protection method according to any embodiment of the present invention.

[0012] Fourthly, the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein when the program instructions are executed by a processor, the processor performs the steps of the active distribution network impedance inverse time protection method according to any embodiment of the present invention.

[0013] The active power distribution network impedance inverse-time protection method and system of this application have the following beneficial effects: The upward arching characteristic compresses the action time of the near-fault point switch to 0.08s to 0.4s, and the remote switch automatically delays. All switches on the line do not need to exchange any information to form a natural time difference. The action time difference between adjacent switches in the same radial direction is calculated by measuring impedance, and the selectivity is guaranteed by the characteristic equation itself.

[0014] Using fault component impedance as the starting criterion, the fault component naturally eliminates the load current during normal operation and the steady-state output of the distributed power source. Its sensitivity to faults is much higher than that of the full electrical quantity. It can reliably detect faults in a very short time after a fault occurs, and is not affected by load fluctuations. It overcomes the problems that the threshold of the full criterion under heavy load conditions is difficult to avoid load fluctuations, and the fault characteristics are weakened under the weak feeder conditions of inverter-type distributed power sources.

[0015] The distributed power supply enhancement effect only increases the measured impedance and delays the action time, without changing the order of the measured impedances of each switch. It will not cause the protection range to shrink or the cascade to malfunction, and the reliable operation of the switch will not be affected. The weak feed characteristic of the inverter power supply does not affect the fault component start-up and full impedance measurement. Combined with the dead-zone-free extension characteristic, the over-limit protection can still operate reliably.

[0016] All switches share a single set of setting parameters. The setting impedance is set according to the longest continuous three downstream sections. Even if the first two switches fail to operate, the current switch can still operate reliably. Only a few parameters such as line unit impedance and section length are required to complete the setting. When a new switch is connected or the topology changes, only one setting impedance needs to be checked according to three sections, which greatly reduces the workload of setting and maintenance.

[0017] The dead-zone-free extension characteristic allows the system to operate within the extension time limit even in the event of an over-limit or high-resistance fault, with the extension time not exceeding 0.8s, thus taking into account the backup requirements for two-stage failure to operate.

[0018] The protection device is installed locally and operates independently, without the need to lay fiber optic channels or synchronize time devices. It can be directly implemented using a primary and secondary integrated pole-mounted circuit breaker. The construction and operation costs are far lower than those of differential protection and other communication-dependent solutions, making it suitable for large-scale application in 10kV active distribution networks.

[0019] The fault direction determination results of each switch are sent up with the action signal. Combined with the line switch topology, the fault section can be quickly located in scenarios where multiple switches trip at the same time or multiple radial path switches trip at the same time. This provides a direct basis for fault isolation and power transfer and restoration of non-faulty sections in centralized feeder automation. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A flowchart illustrating an active power distribution network impedance inverse time protection method according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a 10kV line impedance inverse time protection configuration provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the inverse time-limited action characteristic curve of the upper arch characteristic impedance provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the timing coordination of multiple switches after a fault in pole #118 of the Lumu Line, provided in an embodiment of the present invention. Figure 5 This is a structural block diagram of an active power distribution network impedance inverse time protection system provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Please see Figure 1 The diagram shows a flowchart of an active distribution network impedance inverse time protection method according to this application.

[0024] like Figure 1 As shown, the active distribution network impedance inverse-time protection method specifically includes the following steps: Step S101: The protection devices of each switch along the line collect the voltage and current at the installation point in real time, calculate the fault component impedance, and determine that a fault has occurred and start the protection when the fault component impedance meets the start-up conditions. The fault component impedance is only used for start-up and fault detection and is not used as the distance criterion for inverse time operation.

[0025] In this step, the voltage and current sampling values ​​within a preset time window before the fault occurs are used as the normal voltage and normal current, and the voltage and current sampling values ​​at the current moment after the fault occurs are used as the fault voltage and fault current. The fault component voltage and fault component current are calculated. The fault component voltage is equal to the fault voltage minus the normal voltage, and the fault component current is equal to the fault current minus the normal current. The fault component voltage is divided by the fault component current to obtain the fault component impedance, wherein the fault component impedance excludes the load current during normal operation and the steady-state output of the distributed power source, so that the fault component impedance changes significantly when a fault occurs. The fault component impedance is compared with a preset start threshold. When the amplitude of the fault component impedance is less than the preset start threshold, a fault is determined to have occurred and protection is activated.

[0026] In step S102, the protection device of each switch pre-determines the setting impedance in a uniform manner. The setting impedance is set by multiplying the line impedance of the longest continuous three sections downstream from the protection installation point by a reliability coefficient, so that all switches on the entire line use the same value of the setting impedance.

[0027] In this step, the feeder topology, the positive sequence impedance per unit length of each line segment, and the segment length downstream of each switch installation location are obtained. For each switch, determine the length of the longest three consecutive sections of the line downstream from the installation position of the switch. The three consecutive sections are three consecutive line sections downstream from the section where the switch is located. Multiplying the positive sequence impedance per unit length by the line length and then by the reliability coefficient yields the setting impedance, expressed as: , In the formula, To set the impedance, The impedance per unit length of the line. This refers to the length of the longest three consecutive sections of the line downstream from the switch installation location. The reliability factor, ranging from 0.85 to 0.95, is used to ensure reliable operation while preventing malfunctions under load conditions. Calculate the set impedance of all switches, and take the maximum set impedance of all switches as the unified set impedance for the entire line.

[0028] Step S103: After the fault is started, extract the full voltage phasor and full current phasor at the time of the fault, and calculate the full measurement impedance. The full measurement impedance is used as the distance criterion for inverse time action.

[0029] In this step, after the fault is initiated, the voltage and current sample values ​​at the time of the fault occurrence are extracted based on the time of the fault occurrence. The fundamental phasor of the voltage sample value is extracted as the full voltage phasor using the Fourier algorithm, and the fundamental phasor of the current sample value is extracted as the full current phasor. Both the full voltage phasor and the full current phasor contain amplitude and phase information. The full-scale voltage phasor is divided by the full-scale current phasor to obtain the full-scale measured impedance.

[0030] Step S104: Based on the full-scale measured impedance and the set impedance, the action time is determined using the inverse time equation of the upper arch characteristic impedance, wherein the inverse time equation of the upper arch characteristic impedance is a power function relationship between the action time and the full-scale measured impedance.

[0031] In this step, the time base coefficient is obtained. and minimum action time The time reference coefficient Endpoint action time limit With the minimum action time Determined, wherein the endpoint action time limit The backup protection action time limit is set between 0.5 seconds and 0.8 seconds according to the requirement that the two-stage switch fails to operate. The minimum action time... The setting is based on the inherent tripping time of the circuit breaker and a preset margin. The typical engineering value for the preset margin is 25ms to 50ms, and the time base coefficient is... The expression is: , The full measurement impedance With the set impedance The ratio of the two values ​​is used as the independent variable, and the action time is used as the independent variable. As the dependent variable, the action time is determined according to the inverse time-limited equation of the upper arch characteristic impedance. The expression for the inverse-time equation of the upper arch characteristic impedance is: , In the formula, It is a power exponent and satisfies .

[0032] Step S105: When the full measurement impedance exceeds the set impedance, the protection is not locked. The extension action time is calculated using the inverse time equation of the upper arch characteristic impedance. The extension action time does not exceed the preset endpoint action time limit.

[0033] In this step, when the distributed power source injects boost current into the fault point, the full-scale measured impedance is... Greater than the set impedance When the protection is not locked, the full-measurement impedance will be measured. Substitute the inverse time-limited equation of the upper arch characteristic impedance to directly calculate the extension action time; When the fault passes through the transition resistor, the full-measurement impedance is reduced. Greater than the set impedance When the protection is not locked, the full-measurement impedance will be measured. Substitute the inverse time-limited equation of the upper arch characteristic impedance to directly calculate the extension action time; The extension action time increases with the increase of the full-measurement impedance, but does not exceed the endpoint action time limit. The endpoint action time limit This creates an unprotected dead zone characteristic, ensuring that any fault can eventually be eliminated.

[0034] Step S106: The protection device of each switch is timed independently according to the action time. The full measurement impedance measured by the switch closest to the fault point is the minimum value among all starting switches. The action time corresponding to the minimum value is the shortest action time among all starting switches. The switch corresponding to the shortest action time reaches the action time first and performs tripping.

[0035] In this step, after the switch trips, the fault current disappears. The remaining switches that have been started but have not reached their operating time stop timing and reset because they cannot detect the fault current, thus forming a time difference without communication.

[0036] When the system power supply and distributed power supply feed current into the fault point from multiple directions, the fault can only be cleared when all feed paths are cut off. Switches still flowing with fault current will not reset and will continue to time until they operate. When a fault is fed in from multiple directions, the clearing sequence takes precedence over the differential rule.

[0037] In summary, the method of this application involves real-time acquisition of voltage and current at each switch along the line, and calculation of the fault component impedance as the starting criterion; each switch pre-determines its setting impedance in a unified manner, based on the line impedance of the longest continuous three sections downstream from the protection installation point multiplied by a reliability coefficient; after fault initiation, the full voltage and current phasors are extracted to calculate the full measurement impedance; the operating time is determined according to the inverse-time equation of the characteristic impedance based on the full measurement impedance and the setting impedance; when the measured impedance exceeds the setting impedance, the protection does not block, and the same equation is used to calculate the extended operating time; each switch is timed independently, and the switch closest to the fault point has the shortest operating time and trips first; using fault component initiation and full measurement impedance as distance criteria, the entire line is uniformly set, and a time difference is formed without communication, resulting in fast operation, simple setting, and no protection dead zone, making it suitable for distribution networks with high-penetration distributed power sources.

[0038] In one specific embodiment, such as Figure 2 As shown, the embodiment is the 10kV Lumu line from the Ludong substation. The feeder originates from the 10kV busbar of the substation, with the main line extending from poles #01 to #348. Based on a pole spacing of 60m per level, the total length is approximately 20.9km. The conductor type is JKLYJ-240. The entire line connects 62 public transformers with a capacity of 10.82MV·A. The main line is sequentially equipped with primary and secondary integrated pole-mounted circuit breakers D01 (pole #20), D02 (pole #80), D03 (pole #155), D04 (pole #195), and D05 (pole #240), each equipped with the protection functions of this invention. The lengths of each section are as follows: The distances are 3.6km, 4.5km, 2.4km, 2.7km, and 6.5km. Pole #50 connects to the Wujiashan branch line via a T-junction. Pole #1 of the branch line is equipped with F01, and pole #74 of the branch line is equipped with YS2. The branch line connects to the Wujiashan #1 and #2 hydropower stations (each 400kVA). Pole #79 connects to the Maodian branch line via a T-junction. Pole #1 of the branch line is equipped with F02, and pole #60 of the branch line (hydropower station outlet) is equipped with YS1. The branch line connects to the Maodian hydropower station (200kVA). The total distributed power supply is 1000kVA, with a penetration rate of approximately 9.2%. Each switch protection device independently collects three-phase voltage and current at its installation location, extracts fault components in real time, and starts with the fault component impedance. It completes full-scale impedance calculation, inverse-time timing, fault direction identification, and trip output locally without the need for a communication channel.

[0039] The setting of impedance inverse time protection is performed according to the following steps: S1. Collect feeder topology, line type and positive sequence impedance per unit length z1, length of each section and installation position of each switch, as well as the access location, capacity and fault ride-through characteristics of distributed power sources. S2. Set the setting impedance of each switch, where L is the length of the longest continuous three sections of the line downstream from the protection installation point, and the reliability coefficient is 0.85 to 0.95. All switches on the line have the same value. S3. Determine the endpoint action time limit according to the two-level backup time limit requirement, and take 0.6s within the range of 0.5s to 0.8s; the minimum action time is taken as 0.08s based on the inherent opening time of the circuit breaker; calculate the time base coefficient; S4. Select the power exponent =0.6, generating a uniform inverse time-limited motion equation for the upward arch characteristic across the entire line, the motion characteristic curve is as follows Figure 3 As shown; S5. Under the most unfavorable operating mode of the distributed power source at maximum output (small hydropower provides short-circuit current at 5 times the rated current), verify the measured impedance and sensitivity of each switch when there is a fault at the end of the feeder; verify that the minimum load impedance under the maximum load condition is greater than the set impedance to ensure that the load does not start the protection; verify that the operation time of the extension section of the first two stages of failure to operate and the auxiliary over-limit conditions does not exceed 0.8s. S6. All switches are set to a unified setting value and operate in accordance with the action sequence and reset rules.

[0040] Example: Impedance per unit length of JKLYJ-240 conductor on the Lumu Line ≈0.37Ω / km (impedance angle approximately 64°), calculate the line lengths of the three consecutive downstream sections for each switch: D01 is 10.5km, D02 is 9.6km, and D03 is 11.6km. Take the maximum set impedance among all switches, i.e., set it according to D03 at 11.6km. =0.85, setting impedance ≈0.37 * 0.85 * 11.6 = 3.65 Ω; Take =0.6s =0.08s, calculated =0.52s; take =0.6, action time =0.52·(z) m / 3.65) 0.6 +0.08. The maximum line load is 10.82 MV·A. Based on the minimum operating voltage of 9kV, the minimum load impedance is calculated to be approximately 7.49Ω, which is greater than the set impedance of 3.65Ω. Therefore, the protection will not activate under load conditions. Sensitivity verification: When the most unfavorable fault occurs at the end of this section (3.6km) of switch D01, the impedance is measured. =0.37 * 3.6 = 1.33Ω, sensitivity coefficient The impedance is not less than 1.2, meeting the requirements. Amplification verification: Using the most unfavorable method of injecting 5 times the rated current of a small hydropower station, the amplification coefficient is approximately 1.14, and the verification passes. Two-stage failure-to-operate backup verification: When a fault occurs in section D03 and both D03 and D02 fail to operate, the measured impedance of the third stage D01, including the amplification from Wujiashan and Maodian, is approximately 3.61Ω, exceeding the set impedance. Based on the extended characteristic, the operating time is approximately 0.60s, not exceeding the upper limit of the backup time limit of 0.8s, and the verification passes. The above verifications show that after the set impedance is covered by three consecutive downstream sections, the switch at this stage can still operate reliably when the first two stages fail to operate.

[0041] D02 measured an impedance of 0.84Ω and tripped first after 0.32s, simultaneously cutting off three feeder paths and completely clearing the fault. It should be noted that branch switch F02 only carries the short-circuit current injected by the Maodian Hydropower Station, approximately 58A. However, the section between F02 and the fault point (pole #79-#118) carries the sum of the system power supply and the short-circuit current injected by the two hydropower stations, approximately 2393A, resulting in a boosting ratio of 41 times. Taking this boosting effect into account, the measured impedance of F02 reaches 35.7Ω. Similarly, F01, YS2, and YS1, due to the small current in the Wujiashan branch and significant boosting in the common section, have measured impedances of 15.5Ω, 17.1Ω, and 37.1Ω respectively, all far exceeding the set impedance of 3.65Ω, entering a dead-zone-free extended-ready state. The upstream switch D01 measured 2.37Ω in the forward direction, with a calculated trip time of 0.49s. After D02 trips in 0.32 seconds and the fault current disappears, all the above switches reset. Downstream of the fault point, D03 to D05 experience no fault current and do not start, thus avoiding cascading tripping. In this example, if D02 fails to operate, the switches on each feeder path will continue timing until they operate, and the fault can still be cleared, with no protection dead zone.

[0042] Table 1. Measured impedance and operating time of each switch during a fault at pole #118 on the Lumu Line. .

[0043] In this example, the fault current direction of D01 and D02 is positive, while that of F01, F02, YS1, and YS2 is reverse. There is no fault current in D03 to D05. After each switch sends its action signal and direction mark to the centralized feeder automation master station, the master station locates the fault section according to the following process: Along the power supply path, the last switch that has a positive fault current is D02 (#80 pole). Its adjacent downstream switch D03 (#155 pole) has no fault current passing through it, so the fault section is determined to be the D02 segment (#80 to #155 poles). Although the branch switches such as F01 and F02 are activated due to reverse fault current, their direction marks indicate that they are located on the distributed power supply feed path. Based on this, the master station rules out the possibility that the fault is located on the Wujiashan branch line or the Maodian branch line. Without directional identification, if D02 trips and both branch line switches have fault start information, it will be impossible to directly distinguish whether the fault is located in the D02 section of the main line or any branch line, and manual inspection and confirmation are required. After introducing directional identification, the main station can directly determine the fault section, remotely isolate the D02 section and switch to restore power to the non-faulty section, thus achieving fault self-healing.

[0044] In contrast, if this line adopts a three-stage current protection, the following problems exist under the same fault on pole #118: First, the current setting is based on the short-circuit current under the maximum and minimum operating modes. In this example, the short-circuit current on the system side at the fault point is approximately 2104A, and the two small hydropower stations inject a total of approximately 289A (an increase of approximately 13.7%). The operation and decommissioning of hydropower stations during the wet and dry seasons, as well as changes in power output, cause significant fluctuations in the fault current of each switch, and the protection range expands and contracts accordingly. Under the minimum operating mode, the fault on pole #118 may exceed the protection range of current stage I of D02, requiring instantaneous overcurrent protection (stage II) with a time limit of more than 0.5s to clear the fault. In extreme cases, the sensitivity is insufficient. First, the overcurrent protection system has several drawbacks. First, the time-limit overcurrent protection operates in stages of 0.3s to 0.5s, resulting in a cumulative overcurrent time of over 1.0s for the first-end switches on multi-section lines, leading to long fault clearing times. Second, the reverse feed-in current from the hydropower station flows through branch switches such as F01 and F02, posing a risk of maloperation for current protection without directional measures. Directional elements are required, but small hydropower stations have small capacities, and the reverse fault current is comparable to the load current, making directional element setting and sensitivity verification difficult. Third, the three-stage current protection system does not provide fault direction and section information after operation. When multiple switches trip, fault location relies on manual inspection, making it difficult to support centralized feeder automation and self-healing. A comparison of the two solutions is shown in Table 2.

[0045] Table 2 Comparison of this invention with three-stage current protection (same line, same fault point) , After verification in multiple actual 10kV active distribution network feeder scenarios, this invention can achieve rapid and selective fault clearing under various fault locations and various distributed power supply operation modes. The sensitivity meets the requirements, the two-level fail-to-operate backup time does not exceed 0.8s, and no communication channel is required for the entire line. The overall solution is simple, reliable, and low-cost, making it suitable for large-scale promotion and application.

[0046] Please see Figure 5 The diagram shows a structural block diagram of an active power distribution network impedance inverse time protection system according to this application.

[0047] like Figure 5 As shown, the active distribution network impedance inverse time protection system 200 includes a judgment module 210, a setting module 220, an extraction module 230, a determination module 240, a calculation module 250, and an action module 260.

[0048] The system includes several modules: a judgment module 210, configured to collect real-time voltage and current data at the installation points of each switch along the line, calculate the fault component impedance, and determine a fault and activate protection when the fault component impedance meets the activation conditions. The fault component impedance is used only for activation and fault detection and is not used as a distance criterion for inverse-time operation. A setting module 220 is configured to pre-determine the setting impedance of each switch's protection device in a uniform manner. The setting impedance is set by multiplying the line impedance of the longest continuous three downstream sections from the protection installation point by a reliability coefficient, ensuring that all switches along the line use the same setting impedance value. An extraction module 230 is configured to extract the full voltage phasor and full current phasor at the time of the fault after fault activation, calculate the full measurement impedance, and use the full measurement impedance as a distance criterion for inverse-time operation. A determination module 240 is also included. The system is configured to determine the operating time using the inverse-time equation of the upper-arched characteristic impedance based on the total measured impedance and the set impedance, wherein the inverse-time equation of the upper-arched characteristic impedance is a power function relationship between the operating time and the total measured impedance; the calculation module 250 is configured to not block the protection when the total measured impedance exceeds the set impedance, and to calculate the extended operating time using the inverse-time equation of the upper-arched characteristic impedance, wherein the extended operating time does not exceed the preset endpoint operating time limit; the action module 260 is configured to independently time the protection devices of each switch according to the operating time, wherein the total measured impedance measured by the switch closest to the fault point is the minimum value among all starting switches, the operating time corresponding to the minimum value is the shortest operating time among all starting switches, and the switch corresponding to the shortest operating time reaches the operating time first and performs tripping.

[0049] It should be understood that Figure 5 The modules and references described in the document Figure 1 The steps described in the text correspond to those in the method described above. Therefore, the operations, features, and corresponding technical effects described above also apply to the method described in the text. Figure 5 The various modules in the document will not be described in detail here.

[0050] In other embodiments, the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein when the program instructions are executed by a processor, the processor performs the active power distribution network impedance inverse time protection method in any of the above method embodiments. In one embodiment, the computer-readable storage medium of the present invention stores computer-executable instructions, which are configured as follows: The protection devices of each switch along the line collect the voltage and current at the installation point in real time, calculate the fault component impedance, and determine that a fault has occurred and activate the protection when the fault component impedance meets the activation conditions. The fault component impedance is only used for activation and fault detection and is not used as the distance criterion for inverse time operation. The protection devices of each switch have their setting impedance determined in advance in a uniform manner. The setting impedance is set by multiplying the line impedance of the longest continuous three sections downstream from the protection installation point by a reliability factor, so that all switches on the entire line use the same value of the setting impedance. After the fault is initiated, the full voltage phasor and full current phasor at the time of the fault are extracted, and the full measurement impedance is calculated. The full measurement impedance is used as the distance criterion for inverse time action. Based on the full-scale measured impedance and the set impedance, the action time is determined using the inverse time equation of the upper arch characteristic impedance, wherein the inverse time equation of the upper arch characteristic impedance is a power function relationship between the action time and the full-scale measured impedance; When the full measurement impedance exceeds the set impedance, the protection does not lock out, and the extension action time is calculated using the inverse time equation of the upper arch characteristic impedance. The extension action time does not exceed the preset endpoint action time limit. The protection devices of each switch are timed independently according to the aforementioned action time. The total measured impedance of the switch closest to the fault point is the minimum value among all starting switches. The action time corresponding to the minimum value is the shortest action time among all starting switches. The switch corresponding to the shortest action time is the first to reach the action time and perform tripping.

[0051] Computer-readable storage media may include a stored program area and a stored data area, wherein the stored program area may store an operating system and an application program required for at least one function; the stored data area may store data created based on the use of the active power distribution network impedance inverse-time protection system, etc. Furthermore, the computer-readable storage medium may include high-speed random access memory, and may also include memory, such as at least one disk storage device, flash memory device, or other non-volatile solid-state storage device. In some embodiments, the computer-readable storage medium may optionally include memory remotely configured relative to a processor, and these remote memories may be connected to the active power distribution network impedance inverse-time protection system via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0052] Figure 6 This is a schematic diagram of the structure of the electronic device provided in the embodiment of the present invention, such as... Figure 6 As shown, the device includes a processor 310 and a memory 320. The electronic device may also include an input device 330 and an output device 340. The processor 310, memory 320, input device 330, and output device 340 can be connected via a bus or other means. Figure 6 Taking a bus connection as an example, the memory 320 is the computer-readable storage medium described above. The processor 310 executes various server functions and data processing by running non-volatile software programs, instructions, and modules stored in the memory 320, thereby implementing the active power distribution network impedance inverse-time protection method described in the above embodiment. The input device 330 can receive input digital or character information and generate key signal inputs related to user settings and function control of the active power distribution network impedance inverse-time protection system. The output device 340 may include a display screen or other display device.

[0053] The aforementioned electronic device can execute the method provided in the embodiments of the present invention, and has the corresponding functional modules and beneficial effects for executing the method. Technical details not described in detail in this embodiment can be found in the method provided in the embodiments of the present invention.

[0054] In one implementation, the above-described electronic device is applied to an active power distribution network impedance inverse-time protection system for a client, comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to: The protection devices of each switch along the line collect the voltage and current at the installation point in real time, calculate the fault component impedance, and determine that a fault has occurred and activate the protection when the fault component impedance meets the activation conditions. The fault component impedance is only used for activation and fault detection and is not used as the distance criterion for inverse time operation. The protection devices of each switch have their setting impedance determined in advance in a uniform manner. The setting impedance is set by multiplying the line impedance of the longest continuous three sections downstream from the protection installation point by a reliability factor, so that all switches on the entire line use the same value of the setting impedance. After the fault is initiated, the full voltage phasor and full current phasor at the time of the fault are extracted, and the full measurement impedance is calculated. The full measurement impedance is used as the distance criterion for inverse time action. Based on the full-scale measured impedance and the set impedance, the action time is determined using the inverse time equation of the upper arch characteristic impedance, wherein the inverse time equation of the upper arch characteristic impedance is a power function relationship between the action time and the full-scale measured impedance; When the full measurement impedance exceeds the set impedance, the protection does not lock out, and the extension action time is calculated using the inverse time equation of the upper arch characteristic impedance. The extension action time does not exceed the preset endpoint action time limit. The protection devices of each switch are timed independently according to the aforementioned action time. The total measured impedance of the switch closest to the fault point is the minimum value among all starting switches. The action time corresponding to the minimum value is the shortest action time among all starting switches. The switch corresponding to the shortest action time is the first to reach the action time and perform tripping.

[0055] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of various embodiments or some parts of embodiments.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for inverse-time impedance protection of an active distribution network, characterized in that, include: The protection devices of each switch along the line collect the voltage and current at the installation point in real time, calculate the fault component impedance, and determine that a fault has occurred and activate the protection when the fault component impedance meets the activation conditions. The fault component impedance is only used for activation and fault detection and is not used as the distance criterion for inverse time operation. The protection devices of each switch have their setting impedance determined in advance in a uniform manner. The setting impedance is set by multiplying the line impedance of the longest continuous three sections downstream from the protection installation point by a reliability factor, so that all switches on the entire line use the same value of the setting impedance. After the fault is initiated, the full voltage phasor and full current phasor at the time of the fault are extracted, and the full measurement impedance is calculated. The full measurement impedance is used as the distance criterion for inverse time action. Based on the full-scale measured impedance and the set impedance, the action time is determined using the inverse time equation of the upper arch characteristic impedance, wherein the inverse time equation of the upper arch characteristic impedance is a power function relationship between the action time and the full-scale measured impedance; When the full measurement impedance exceeds the set impedance, the protection does not lock out, and the extension action time is calculated using the inverse time equation of the upper arch characteristic impedance. The extension action time does not exceed the preset endpoint action time limit. The protection devices of each switch are timed independently according to the aforementioned action time. The total measured impedance of the switch closest to the fault point is the minimum value among all starting switches. The action time corresponding to the minimum value is the shortest action time among all starting switches. The switch corresponding to the shortest action time is the first to reach the action time and perform tripping.

2. The active distribution network impedance inverse-time protection method according to claim 1, characterized in that, The protection devices of each switch along the line collect the voltage and current at the installation point in real time, calculate the fault component impedance, and determine that a fault has occurred and activate the protection when the fault component impedance meets the activation conditions, including: Using the voltage and current sampling values ​​within a preset time window before the fault occurs as the normal voltage and normal current, and using the voltage and current sampling values ​​at the current moment after the fault occurs as the fault voltage and fault current, calculate the fault component voltage and fault component current. The fault component voltage is equal to the fault voltage minus the normal voltage, and the fault component current is equal to the fault current minus the normal current. The fault component voltage is divided by the fault component current to obtain the fault component impedance, wherein the fault component impedance excludes the load current during normal operation and the steady-state output of the distributed power source, so that the fault component impedance changes significantly when a fault occurs. The fault component impedance is compared with a preset activation threshold. When the amplitude of the fault component impedance is less than the preset activation threshold, a fault is determined to have occurred and protection is activated. The fault component impedance is used only for the startup and fault detection stages and is not used as the distance criterion for inverse time-limited action. The distance criterion is the full-quantity measured impedance.

3. The active distribution network impedance inverse-time protection method according to claim 1, characterized in that, The protection devices of each switch have their setting impedance predetermined in a uniform manner. The setting impedance is determined by multiplying the line impedance of the longest continuous three sections downstream from the protection installation point by a reliability factor, including: Obtain information on the feeder topology, the positive sequence impedance per unit length of each line segment, and the segment length downstream of each switch installation location; For each switch, determine the length of the longest three consecutive sections of the line downstream from the installation position of the switch. The three consecutive sections are three consecutive line sections downstream from the section where the switch is located. Multiplying the positive sequence impedance per unit length by the line length and then by the reliability coefficient yields the setting impedance, expressed as: ， In the formula, To set the impedance, The impedance per unit length of the line. This refers to the length of the longest three consecutive sections of the line downstream from the switch installation location. The reliability factor, ranging from 0.85 to 0.95, is used to ensure reliable operation while preventing malfunctions under load conditions. Calculate the set impedance of all switches, and take the maximum set impedance of all switches as the unified set impedance for the entire line.

4. The active distribution network impedance inverse-time protection method according to claim 1, characterized in that, The extraction of the full voltage phasor and full current phasor at the moment of the fault, and the calculation of the full measurement impedance, include: After the fault is initiated, the voltage and current sample values ​​at the time of the fault occurrence are extracted based on the time of the fault occurrence. The fundamental phasor of the voltage sample value is extracted as the full voltage phasor using the Fourier algorithm, and the fundamental phasor of the current sample value is extracted as the full current phasor. Both the full voltage phasor and the full current phasor contain amplitude and phase information. The full-scale voltage phasor is divided by the full-scale current phasor to obtain the full-scale measured impedance.

5. The active distribution network impedance inverse-time protection method according to claim 1, characterized in that, The step of determining the action time using the inverse time equation of the upper arch characteristic impedance based on the full-measurement impedance and the set impedance includes: Obtaining time base coefficients and minimum action time The time reference coefficient Endpoint action time limit With the minimum action time Determined, wherein the endpoint action time limit The backup protection action time limit is set between 0.5 seconds and 0.8 seconds according to the requirement that the two-stage switch fails to operate. The minimum action time... The time reference coefficient is set according to the inherent tripping time and preset margin of the circuit breaker. The expression is: ， The full measurement impedance With the set impedance The ratio of the two values ​​is used as the independent variable, and the action time is used as the independent variable. As the dependent variable, the action time is determined according to the inverse time-limited equation of the upper arch characteristic impedance. The expression for the inverse-time equation of the upper arch characteristic impedance is: ， In the formula, It is a power exponent and satisfies .

6. The active distribution network impedance inverse-time protection method according to claim 5, characterized in that, When the total measured impedance exceeds the set impedance, the protection does not lock out, and the extended action time is calculated using the inverse time equation of the upper arch characteristic impedance, including: When the distributed power source injects boost current into the fault point, the full-measured impedance is reduced. Greater than the set impedance When the protection is not locked, the full-measurement impedance will be measured. Substitute the inverse time-limited equation of the upper arch characteristic impedance to directly calculate the extension action time; When the fault passes through the transition resistor, the full-measurement impedance is reduced. Greater than the set impedance When the protection is not locked, the full-measurement impedance will be measured. Substitute the inverse time-limited equation of the upper arch characteristic impedance to directly calculate the extension action time; The extension action time increases with the increase of the full-measurement impedance, but does not exceed the endpoint action time limit. The endpoint action time limit This creates an unprotected dead zone characteristic, ensuring that any fault can eventually be eliminated.

7. An active power distribution network impedance inverse-time protection system, characterized in that, include: The judgment module is configured to collect the voltage and current at the installation point of each switch along the line in real time, calculate the fault component impedance, and determine that a fault has occurred and start the protection when the fault component impedance meets the start-up conditions. The fault component impedance is only used for start-up and fault detection and is not used as the distance criterion for inverse time operation. The setting module is configured to pre-determine the setting impedance of the protection device of each switch in a uniform manner. The setting impedance is set by multiplying the line impedance of the longest continuous three sections downstream from the protection installation point by a reliability coefficient, so that all switches on the entire line adopt the same value of the setting impedance. The extraction module is configured to extract the full voltage phasor and full current phasor at the time of the fault after the fault is started, and calculate the full measurement impedance. The full measurement impedance is used as the distance criterion for inverse time action. The determination module is configured to determine the action time based on the full-scale measured impedance and the set impedance using the inverse time equation of the upper arch characteristic impedance, wherein the inverse time equation of the upper arch characteristic impedance is a power function relationship between the action time and the full-scale measured impedance; The calculation module is configured such that when the full measurement impedance exceeds the set impedance, the protection does not lock out, and the extension action time is calculated using the inverse time equation of the upper arch characteristic impedance, wherein the extension action time does not exceed the preset endpoint action time limit. The action module is configured such that the protection devices of each switch are timed independently according to the action time. The total measured impedance of the switch closest to the fault point is the minimum value among all starting switches. The action time corresponding to the minimum value is the shortest action time among all starting switches. The switch corresponding to the shortest action time is the first to reach the action time and perform tripping.

8. An electronic device, characterized in that, include: At least one processor, and a memory communicatively connected to the at least one processor, wherein the memory stores instructions executable by the at least one processor to enable the at least one processor to perform the method according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by a processor, it implements the method described in any one of claims 1 to 6.

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